1. Field of the Invention
The present invention relates to an apparatus for and method of recording information on a recording medium that enables additional recording of information thereon.
2. Description of the Related Art
A write once (WO) type optical disk and rewritable (RW) type optical disk are recording media that enable additional recording of information thereon. The WO type disk is a disk that enables information to be written only once at the same portion thereof. The RW type optical disk is a disk that enables information to be written many times at the same portion thereof.
In an information recording apparatus that writes information data onto a disk enabling additional recording of information, when information data is written onto a disk, a write clock signal is produced. The information recording apparatus then writes information data onto the disk while making a synchronization (e.g., bit synchronization) between the thus-produced and stable write clock signal having a predetermined frequency and the writing operation of writing information data onto the disk. This write clock signal in general is produced by a reference clock generator such as a crystal oscillator enabling the independent generation of an oscillation output.
However, in a case where additionally recording new information data onto the disk in which information data is already partly or locally written, in such a way that the new information data is written successively to this already written information data, there is the possibility that the write clock signal that was used for recording of the already written information data and the write clock signal that is used for recording of the new information data will fall out of phase.
In this case, when performing an operation of reading information data from a disk on which new information data has been written successively to the already written information data, it is difficult to reproduce a synchronization clock signal at or around a portion of connection between the preceding and the succeeding information data. If the synchronization clock signal cannot be reproduced correctly, the information data cannot be read correctly.
Especially, if information data is firstly written onto the disk by a information recording apparatus, and thereafter, another information data is successively written onto the same disk by a different information recording apparatus, the former information data and the later information data are recorded according to two different write clock signals, respectively. Even if the types of those information recording apparatus are the same, the write clock signals generated in the respective information recording apparatuses are actually different from each other not only in phase but also in frequency.
In order to reproduce a synchronization clock signal to be used for reading information data, a PLL (Phase Locked Loop) circuit is used if preceding data and succeeding data are written onto the disk according to different write clock signals, respectively, the synchronizing operation of the PLL circuit is largely disturbed at or around the portion of connection between such preceding data and succeeding data, when reproducing these data. As a result of this, there is the possibility that a decoder for performing decoding processing of the read data according to the synchronization clock signal of it will inconveniently make an erroneous detection of various data items in the read data.
Also, generally, information data to be written onto a disk is divided into information blocks each having a prescribed size, and a particular synchronization signal is added to each of the information blocks. Accordingly, when reproducing information data from the disk, it is also possible to establish a synchronization based on the particular synchronization signal added to each information block, as well as to make a bit synchronization such as that mentioned above. However, such a particular synchronization signal is also inherently one which has been recorded in the disk with a timing based on the write clock signal. Accordingly, if a preceding particular synchronization signal and succeeding particular synchronization signal are written onto the disk using write clock signals different from each other in phase or frequency, the periodic continuity can not be still obtained.
For example, there is a case where the interval between a particular synchronization signal added to a rearmost region of the preceding information block and a particular synchronization signal added to a foremost region of the succeeding information data irregularly varies due to the difference between the write clock signals. In this case, there is the possibility that when performing reproduction, such difference will be followed by a failure of detection or an erroneous detection.